1. Field of the Invention
The present invention relates to a knitted or woven cloth having antistatic properties which is suitable for use in the preparation of filter bags or garments. More particularly, this invention relates to a knitted or woven cloth which contains an electrically conductive thread composed of 10 to 90 weight % of electroless metal plated staple fibers, and 90 to 10 weight % of metallic filaments, in a specific amount.
2. Description of Prior Art
When large quantities of electrically chargeable powdered materials, such as certain powdered high polymers or certain powdered inorganic materials, are handled, or when such materials are treated under high speeds, their characteristic of picking up static electricity can cause processing difficulties.
For instance, in certain chemical filtering operations, in which powdered particles are brought into mutual frictional contact, or into frictional contact with the filter bag, the build-up of static electricity can be so great, that static electricity discharge can cause severe shocks to workers, or can cause dust explosions. In other instances, the build-up of electrical charges in the particles or on the filter bag can impede the filtering operation.
Another instance of difficulties which can be caused by the accumulation of static electrical charges is in certain coating processes, such as in the manufacture of kraft papers. Again, shocks due to static electricity discharge can be annoying or injurious to workers or, in severe instances, can induce explosions. In this instance, the static electricity build-up is caused by the frictional movement of the work product beneath the coating apparatus, such as the feed rollers.
There is a need, therefore, for a means of removal of static electrical charges during such chemical processing.
In U.S. Pat. No. 3,288,175, it is suggested to solve the static electricity problem in such processes, by carrying out the processes in contact with a cloth containing metallic fibers. The use of such cloth as the filter medium, or as the base or surface of the feed rolls in contact with the work being coated, however, has not proven to provide adequate antistatic properties.
It is also known from U.S. Pat. No. 2,845,962, to provide an antistatic textile by the use of fibers which contain carbon black dispersed therein, and thus which are electrically conductive. However, in this case, the desired conductivity cannot be obtained unless a substantial amount of carbon black is dispersed throughout the interior of the fiber, which has the effect of reducing the mechanical strength of the fiber and rendering it susceptible to rupture during use.
Another prior art proposal was to incorporate into the cloth a small amount of electrically conductive fibers which had been prepared by coating the fiber with a resinous matrix and finely divided silver or carbon black (U.S. Pat. No. 3,586,597). However, this expedient also has been found to provide insufficient antistatic properties.
A need continues to exist, therefore, for an antistatic cloth which can be used in the preparation of filter bags or garments, which is characterized by a high level of antistatic properties, and which is characterized by good strength properties.